The present invention relates to a container coating process and more particularly to a process for coating the base of a bottle in selected areas to prevent shattering and fragment scatter.
Glass containers, such as glass bottles, have long been used as receptacles for soft drinks and various other commodities since they are superior in many respects to other types of containers. Glass containers can be formed in a wide variety of shapes and sizes. Additionally, glass containers are easily sanitized. The recent growth in interest in energy conservation and in resource conservation has increased the attractiveness of glass containers since these containers are easily cleaned and sterilized and are therefore easily reused. Glass containers are relatively sturdy and will hold up through a number of recyling operations although, after approximately 10 cycles, abrasion marks on the glass show and the glass looses its intrinsic strength.
One substantial drawback to the glass container is its tendency to shatter upon impact with a hard surface producing sharp glass shards. The safety risk involved with such breakage is heightened by the fact that many glass containers are pressurized (such as bottles containing carbonated beverages) and the shards which result from shattering the glass container will be scattered over a relatively large area. It has been determined that coating glass bottles with various plastic materials can significantly reduce shattering and reduce the scattering of glass shards. It has also been determined that a suitable coating properly applied to glass bottles will reduce the abrasion marks and reduce breakage during the filling and handling process, thereby increasing the number of times a glass container can be recycled. These techniques also permit a reduction in the amount of glass in the bottle and therefor lighter bottles.
Various techniques and materials have been developed, for coating glass containers such as glass bottles (see, for example, U.S. Pat. Nos. 4,092,953; 4,207,356 and 4,225,638). The base of the glass bottle presents an unusual coating problem. Normally, bottles containing carbonated beverages and the like are filled and shipped standing on their base. As a result, a typical soft drink bottle contains thicker glass in its base than in its side wall such that the base can withstand the frequent collisions which occur as the bottles are conveyed along a production line and when the bottles are loaded into shipment containers, shipped and stacked on the grocers shelf. At the same time, because the base of a typical glass bottle is thicker, the base does not shatter to the same extent when the bottle breaks but large pieces of glass blow out from the base of the bottle.
In some cases, it is possible to leave the base uncoated and rely upon the side coating to hinge the base pieces to the bottle sides when blow out occurs. This is particularly true since an overall base coating is less desirable than no coating at all. One means that has been used to bottom coat a bottle is to dip the base of the bottle into a bath of resin. This is undesirable, however, because the bearing surface is coated with resin and the coating, particularly on the bearing surface, is frequently marred, gouged, rubbed, and worn as the bottle rides on the base through cleaning, filling and shipping. This introduces lines of weakness in the coating on the bottle which leads to its easy rupture on being dropped. Furthermore, when the sides and base are coated with a continuous layer of plastic, the coating on the sides of the bottle may peel off if the coating is marred, worn or broken on the bearing surface. In particular, when the bottles are washed in caustic for reuse, the caustic will attack breaks in the coating at the bearing surface, leading to early coating failure.
Thus, there is a need for a coated base in which the bearing surface is not coated for use with larger bottles having large bases in which pieces of base glass are not hinged to the side coating when the bottle breaks and for use with lighter weight bottles which do not contain large volumes of glass in the base. There is also a need for a bottom coating process which is capable of coating only select areas of the base as required to prevent fragment scattering.